Incredible phenomena will occur...

Illinois was hit with an EF4 (preliminary rating) tornado this week, which killed 6 people and did untold millions in damages.

Here’s what an EF4 rating means. Meteorologists use the Enhanced Fujita (EF) scale to grade tornadoes based on their estimated wind speeds. Wind speeds are not measured (because measurement equipment is not around when a tornado touches down, plus it would be very dangerous to make a measurement) they are estimated based on the kind of damage the tornado causes.

An EF4 is a very powerful beast, the second most powerful rating. The EF scale does not indicate tornado size, but there is a correlation between wind speed and size, generally the size goes up as the EF rating does. There have been EF5 tornados measured at a mile wide. Tornados also get faster as they get bigger, a large one can move across the land at more than 70 MPH and travel more than 200 miles.

Here are the ratings, along with their observed types of damage:

EF0: 65-85 mph. Light damage. Some damage to chimneys; branches broken off trees; shallow-rooted trees pushed over; signboards damaged.

EF1: 86-110 mph. Moderate damage. Peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos blown off roads.

EF2: 111-135 mph. Considerable damage. Roofs torn off frame houses; mobile homes demolished; boxcars overturned; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground.

EF3: 136-165 mph. Severe damage. Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; heavy cars lifted off the ground and thrown.

EF4: 166-200 mph. Devastating damage. Well-constructed houses leveled; structures with weak foundations blown away some distance; cars thrown and large missiles generated.

EF5: 200+ mph. Incredible damage. Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 meters (109 yds); trees debarked; incredible phenomena will occur.